GB1381734A - Alarm systems - Google Patents

Abstract

1381734 Alarm systems BALDWIN ELECTRONICS Inc 30 Dec 1971 [31 Dec 1970] 60832/71 Heading G4H In a radio alarm system comprising a central station and plurality of peripheral stations, detection of an alarm condition at a peripheral station causes it to generate a pulse train representing a sequence of substantially identical frames of data following one another without pause, each frame commencing and terminating with identical master pulses of width different from the other pulses in the train, the commencing master pulse of each succeeding frame being constituted by the terminating master pulse of the preceding frame, there being between the master pulses of a given frame a fixed predetermined number of data pulses some at least of which are modulated in time position to constitute a multi-digit coded number identifying the peripheral station, the sequence of frames being transmitted by radio to the central station wherein the data is received, decoded and stored. As disclosed, there are four data pulses per frame, the time interval between the (leading edge of the) commencing master pulse and the first data pulse identifying one of ten alarm detectors at the peripheral station, and that between the first data pulse and the second, that between the second and the third, that between the third and the fourth and that between the fourth and the terminating master pulse specifying the four decimal digits of the peripheral station identity respectively. Each alarm detector includes a bi-stable which is set by the alarm condition and can be reset manually or after 3 minutes, provided the alarm condition has been remedied, the use of the bistable preventing repeated outputs from an alarm detector for the same alarm condition. An output from any of the ten alarm detectors at the peripheral station turns on the power supply to the rest of the station for 3 minutes, and keys on a transmitter for 6 periods of 10 seconds, separated by 20-second gaps, the frame being sent 10 times per 10-second period. A decoded count is used to sample a resistor in the alarm detector followed by four further resistors, the five resistors providing amplitudesignificant voltages which by means of an integrator and thresholder produce timed pulses constituting the frame pulses. An oscillator provides one frequency for pulses and another for gaps between pulses, the frequencies passing to the transmitter via a modulator. Two lamps at the peripheral station indicate " at least one detector on " and " all detectors off" respectively. At the central station, the five intervals in the frame are measured by counting clock pulses, six counters being provided, two of these being used alternately for the first interval of successive frames. The counts are stored, displayed on lamps and printed out. An audible alarm can be given if several data frames (i.e. from different peripheral stations) are coupled to the lamps together. A test is possible by feeding the clock pulses to a series arrangement of the counters for one second, a visual check being made of the counts displayed.